NaiveTicket

NaiveTicket

The second Objects lab,from the BlueJ book's second chapter.

Look for the Chapter 2 file you need in the doc folder. There is 35 pages of reading and exercises in the chapter.

Work through all these exercises. You edit this file with your answers for these exercises.

• Exercise 2.1 Create a TicketMachine object on the object bench and take a look at its methods. You should see the following: getBalance, getPrice, insertMoney, and printTicket. Try out the getPrice method. You should see a return value containing the price of the tickets that was set when this object was created. Use the insertMoney method to simulate inserting an amount of money into the machine and then use getBalance to check that the machine has a record of the amount inserted. You can insert several separate amounts of money into the machine, just like you might insert multiple coins or notes into a real machine. Try inserting the exact amount required for a ticket. As this is a simple machine, a ticket will not be issued automatically, so once you have inserted enough money, call the printTicket method. A facsimile ticket should be printed in the BlueJ terminal window.

• Exercise 2.2 What value is returned if you check the machine’s balance after it has printed a ticket?

• Exercise 2.3 Experiment with inserting different amounts of money before printing tickets. Do you notice anything strange about the machine’s behavior? What happens if you insert too much money into the machine – do you receive any refund? What happens if you do not insert enough and then try to print a ticket?

• Exercise 2.4 Try to obtain a good understanding of a ticket machine’s behavior by interacting with it on the object bench before we start looking at how the TicketMachine class is implemented in the next section.

• Exercise 2.5 Create another ticket machine for tickets of a different price. Buy a ticket from that machine. Does the printed ticket look different? The ticket does change the price.

• Exercise 2.6 Write out what you think the outer wrappers of the Student and LabClass classes might look like – do not worry about the inner part.

• Exercise 2.7 Does it matter whether we write public class TicketMachine or class public TicketMachine in the outer wrapper of a class? Yes, it does matter to write 'public class TicketMachine.'

Edit the source of the TicketMachine class to make the change and then close the editor window. Do you notice a change in the class diagram? The class diagram does have brown cross strips, once I had closed the editor window.

What error message do you get when you now press the Compile button? "Invalid method declaration; return type is required"

Do you think this message clearly explains what is wrong? No this message does not clearly explain what is wrong with it could have elaborated more.

• Exercise 2.8 Check whether or not it is possible to leave out the word public from the outer wrapper of the TicketMachine class. I have checked it does not produce any syntax error. I believe by default it would be marked as public?

• Exercise 2.9 From your earlier experimentation with the ticket machine objects within BlueJ you can probably remember the names of some of the methods – printTicket, for instance. Look at the class definition in Code 2.1 and use this knowledge, along with the additional information about ordering we have given you, to try to make a list of the names of the fields, constructors, and methods in the TicketMachine class. Hint: There is only one constructor in the class. fields(instance variables)--price, balance and total constructors--TicketMachine methods--getPrice, getBalance, insertMoney and printTicket

Exercise 2.10 Do you notice any features of the constructor that make it significantly different from the other methods of the class? constructor--initiates value assigned in the fields and takes parameters.

• Exercise 2.11 What do you think is the type of each of the following fields? private int count; private Student representative; private Server host;

int

• Exercise 2.12 What are the names of the following fields?

  private boolean alive;
  private Person tutor;
  private Game game;
  

  boolean

• Exercise 2.13 In the following field declaration from the TicketMachine class

  private int price;
  

  does it matter which order the three words appear in? Yes, it does matter the order the three words appear in as type and being it giving the access to public or not needs to appear before the name of the variables.

Edit the TicketMachine class to try different orderings. After each change, close the editor. Does the appearance of the class diagram after each change give you a clue as to whether or not other orderings are possible? The class diagram for the TicketMachine did not change at all.Changing the private keyword between int and price or balance gave me identifier error.p private at the end gave me "illegal start of type"

Check by pressing the Compile button to see if there is an error message.

Make sure that you reinstate the original version after your experiments!

• Exercise 2.14 Is it always necessary to have a semicolon at the end of a field declaration? Once again, experiment via the editor. The rule you will learn here is an important one, so be sure to remember it. "';' expected" -- Yes it is very much important have semicolon at the end of a field variable declaration.

• Exercise 2.15 Write in full the declaration for a field of type int whose name is status.

• Exercise 2.16 To what class does the following constructor belong?

  public Student(String name)
  

  Belongs to class Student

• Exercise 2.17 How many parameters does the following constructor have and what are their types?

  public Book(String title, double price)
  

  it has two parameters title and price.

• Exercise 2.18 Can you guess what types some of the Book class’s fields might be? Can you assume anything about the names of its fields?

It could be types int or double

Work all Exercises from 2.19 to 2.58 that are NOT marked Challenge exercise. READ upto and INCLUDING section 2.15 of this chapter.